The present invention relates to novel pigments, and in particular, pigments that have been treated with certain organo-acid phosphate compounds.
The incorporation of pigments into polymer matrices has been performed for many years, and over the years, pigments have been and continue to be incorporated into polymers matrices for many reasons. For example, pigments may be used as fillers. They may also be used to impart better physical and chemical attributes to polymer matrices, including improved thermal stability, especially lacing resistance in extruded polymer film applications, and decreased chemical activity. In order to obtain different benefits, pigments may be treated in different ways, including by adding surface treatments.
Commonly used pigments include titanium dioxide, kaolin and calcium carbonate. Commonly known surface treatments that have been applied to pigments include silanes, alkylphosphonic acids and phosphorylated polyenes. The precise attributes that one wants in a treated pigment will depend in part on the application in which it will be used. Often one wants to provide a hydrophobic pigment that is stable, easy to prepare, cost effective, can be dispersed to a high degree in polymers, and does not react in the presence of other additives such as lithopone.
However, despite the numerous known surface treatments, for various reasons, including cost and desired properties, no known surface treatments are ideal for all applications. Thus, there is always a need to develop new and better treatments for pigments.
One under-explored option for treating pigments is the use of esters of phosphoric acids. These compounds have been suggested to mix with pigments and to form suspensions in, for example, aqueous coatings applications. However, such a use produces a unique product that may be used in a unique application. Thus, the limited teachings for use of esters of phosphoric acids in aqueous coatings applications do not suggest the pigments treated with low levels of organo-acid phosphates of this invention or that the pigments treated with low levels of organo-acid phosphates of this invention would have utility in plastics.
The present invention provides economical and easily prepared novel pigments that possess resistance to lacing when incorporated into polymeric articles (such as films), do not produce objectionable side reactions when mixed with common plastics additives such as lithopone, which contains zinc sulfide, and are stable such that they possess low levels of extractable organics. Durable plastics products that incorporate the treated pigments of the present invention resist yellowing when phenolic-type antioxidants are used. In addition, a polymer matrix containing up to about 85% of organo-acid phosphate treated titanium dioxide pigment, based on the weight of the polymer may be produced. The polymer matrix may be an end-product in and of itself or a product that will be further processed such as in a masterbatch, which can be let down into a polymeric film.
The present invention provides novel treated pigments for use in polymer matrices. The treated pigments of the present invention are organo-acid phosphate treated compounds comprising a pigmentary base that may be treated with the reaction products of: (1) at least one organic alcohol; and (2) P2O5 and/or phosphoric acid. The phrases xe2x80x9cat least one organic alcoholxe2x80x9d and xe2x80x9corganic alcoholsxe2x80x9d mean one or more types of organic alcohols, for example, a solution of hexanol or octanol or a mixture of hexanol and octanol. The organic alcohols, P2O5 and phosphoric acid are selected such that their reaction products include an organo-acid phosphate that may be represented by the formula:
xe2x80x83(Rxe2x80x94O)xPO(OH)y
wherein
x=1 or 2;
y=3xe2x88x92x; and
R is an organic group having from 2 to 22 carbon atoms.
Alternatively, one may start with the organo-acid phosphate directly if it is available, rather than produce it from the reactants described above.
The treated pigments of the present invention may be combined with and readily dispersed into polymers to form polymer matrices. These polymer matrices have improved physical properties such as impact strength, tensile strength and flexural characteristics.
The treated pigments of the present invention may also be used to prepare highly loaded polymer masterbatches. These highly loaded masterbatches are especially useful in applications in which dispersion and thermal stability, especially resistance to lacing, are critical.
Based on the foregoing, there is still a need for better treated pigments. The treated pigments of the present invention have the advantages of being hydrophobic pigments that are stable, easy to prepare, cost effective, can be dispersed to a high degree in polymers, and do not react in the presence of other additives such as lithopone. Such treated pigments may be useful in the manufacture of plastics and other products.